1. Field of the Invention
The invention relates generally to covers for trim components in a vehicle passenger compartment and more specifically to vehicular trim components with covers comprising composite stitching.
2. Description of the Related Art
Trim components, such as door armrests, center console armrests, and gear shifter boots, for a vehicle passenger compartment of luxury vehicles typically have a leather exterior surface, and leather is often an upgrade option for other vehicles. Leather is considered a highly desired and superior cover material because of its sleek appearance and distinguishable texture. The premium that consumers pay for leather surfaces arises not only from the higher material cost, but also from the manufacturing and assembly costs.
Usually, the leather cover on a trim component comprises two or more pieces of leather that are individually cut and sewn together with a manually operated sewing machine in several steps. To join two pieces of leather 100 and 102, as illustrated in FIG. 1, the pieces 100 and 102 are layered with the exterior leather surfaces 104 facing each other, and a butt seam 106 is sewn along the pieces 100 and 102 at a predetermined distance, approximately one centimeter, from the edge. After the butt seam 106 is in place, the pieces 100 and 102 are folded away from each other such that the two exterior leather surfaces 104 form one continuous surface, which can be seen in FIG. 2, with a crease at the interface of the pieces 100 and 102. The thread of the butt seam 104 is not visible from the exterior when the pieces 100 and 102 are folded open. To provide a refined appearance, the inside edges 108 and 110, which are the portions of the pieces 100 and 102 that are approximately one centimeter wide, are folded away from each other and sewn to their respective pieces of leather 100 and 102, as shown in FIG. 3. The resulting seams 112 and 114 are parallel to and spaced from the butt seam 106. The three seams—the butt seam 106 and the two parallel seams 112 and 114 are known as a French seam 116 and are characteristic of leather covers for vehicular trim components.
After all the pieces of the leather are sewn together with French seams 116 to form a cover 118, the cover 118 is assembled to a rigid shell 120 to construct the vehicular trim component 122, as shown in FIGS. 4A and 4B. The rigid shell 120 is commonly composed of a polymer material or composite material and provides structural support for and defines the shape of the trim component 122. Cushioning, usually a foam layer (not shown) shaped to mate with the shell 120, is positioned over the shell 120, and the leather cover 118 is manually placed over the cushioning and hand-wrapped around the rigid shell 120. The leather cover 118 is stapled to the shell 120, by hand, around the entire edge of the cover 118, as best seen in FIG. 4B. Although the staples are not visible when the trim component 122 is installed in the vehicle compartment, the stapling process requires expensive manual labor and is very time consuming. Furthermore, leather covers 118 cannot be shaped to cover portions of the shell 120 having a small surface area or a complex shape, such as a pull cup 124 in door armrests. As a result, the leather surface trim component 122 is actually a composite component having leather and polymer surfaces.
In an effort to manufacture affordable trim components having the appearance of “cut and sew” hand-wrapped leather products, trim component manufacturers have turned to polymer molding processes. During such processes, molten polymer material, for example a polyvinyl chloride (PVC) or a thermoplastic elastomer (TPE), is injected into a mold, where it solidifies into a part having the shape of the mold. Molds for faux leather trim covers comprise a surface with a texture similar to leather and features resembling French stitching. While the surface texture and butt seams of molded products closely resemble the corresponding aspects of “cut and sew” hand-wrapped leather products, the molded seams parallel to the butt seam have an obvious faux appearance. The absence of thread in the parallel seams is an immediate indicator that the seam is a molded French seam and, therefore, the trim component does not have a leather surface.